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What are the steep ramps often erected at large airports?
For example, the following white and orange striped ramp:

I've seen these at a couple large airports but I've never seen them actually used for anything.

Here in the United States these are called blast fences.  They protect whatever may be behind them from the direct effects of jet blast by directing the blast upwards.

Airports do have blast fences for the purpose that you mention, but the barrier in this picture appears to just be a barricade blocking a closed taxiway, not a blast fence. Blast fences are typically taller than that and, at least in the case of most of the ones I've seen, aren't painted (though they do often have red lights on the top to help pilot see and avoid them when landing or taxiing.)

Apart from blast fences, they also serve as wind breaks and to deflect engine noise away from the area behind them.
And of course they can (and the one you showed looks like it might be) intended to be a visible marker of a closed taxiway or runway.

If you've ever watched an aircraft carrier launch a plane, you'll see such a barrier pop up (on hinges) right behind the jet exhaust to deflect it upward and away from other aircraft and deck crew behind the launch catapult.
These things (picture above) look pretty heavy, so they won't be blown over easily. I doubt they would use them to mark a closed runway, unless it's quite long term, as they would be difficult to move around. Does anyone know if they are in fact lightweight, and attach to the runway in some manner?

likely concrete blocks that a forklift can move (of the same type you'd see during highway construction)

I wonder if skateboarders ever try to sneak in and do "quarter-pipe" maneuvers on them?  Anyway, even if a forklift can move them (temporary runway closure), it would still be a hassle. Plus, they would be quite damaging if an aircraft were to accidentally plow into them while landing/taking off, or even just taxying. Aren't closed runway markers supposed to be lightweight and frangible?

@PhilPerry these things are. They're basically steel frames with metal sheeting bolted on, they're not solid.

The following is speculation, as I have no specific knowledge on the matter, but searching a bit it seems that they are needed for deflecting upwards the engine blast
http://www.bdi.aero/
Also, it seems from that website that they also provide a minimum of noise abatement.

http://en.wikipedia.org/wiki/Jet_blast_deflector

+1 I can't understand why your answer provided in the 10 minutes after the question was published has not been selected/upvoted more. The currently selected says less and was written 24 hours after...

Link-only answers are not good, can you at least expand on their point here onsite? Is it only when taxiways (esp. with small planes) pass near start of a large runway (with large planes)? (How near, what size plane on the large runway, how much thrust?) Is it mainly for safety rather than noise pollution? Does it depend if there's populated land or water in the direct path behind the large runway? etc etc.

@smci this is not a link only answer and those extra points are separate questions.


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Can fuzzy dice help in IMC?
Just had this thought as I’ve read about multiple GA accidents that resulted from unintentional flight into IMC with planes not equipped for it (no attitude indicator), resulting in disorientation and other things.
So, that said, would something low-tech like fuzzy dice, rosary beads, air freshener, etc. hanging from overhead help alleviate those issues if one unintentionally flew into those conditions? Help alleviate in this sense would mean help limit disorientation and assist in correcting pitch and/or roll in the absence of instruments.

Usually fuzzy dice hanging from the rear-view mirror just block the view of the road. This is the first time I've ever heard of even the possibility of them being somehow useful...

Think about the forces acting on the dice in various flight maneuvers.  How would they affect their “proper” indication.   Bottom line they would only be accurate in unaccelerated flight.  So first you’d need help getting to that state.

Ah yes, that seems like the same thing. Didn’t know how exactly to word it to find dupes.

The number of planes that don't have an attitude indicator is extremely small, probably limited to ultralights without an enclosed cockpit (where your fuzzy dice get blown backwards by the wind)

@FreeMan if your car is upside-down, you may have bigger problems than windscreen visibility.

This question can't not be a duplicate.  Unfortunately the plumb bob would tell you the same thing your inner ear is telling you, because they are acted upon by the same forces!  And as you know, the inner ear is wrong because it's not a gyroscope.   If the plumb bob was a gyroscope, however...

@DJClayworth - most club-owned glider towplanes (as well as most gliders) lack functioning attitude indicators.  Likely also true of most purpose-designed aerobatic aircraft.  Also true of the Taylorcraft  I got my license in and the Ces 12O I rented after that.

And that's why I made sure to practice "partial panel" cloud flying- all cloud flying was "partial panel" in those planes!

No.
The simple fact is, any kind of hanging indicator would be subject to the same G forces that confuse a human's inner ear. Here's a famous video of pilot Bob Hoover pouring tea while doing a barrel roll. If you look carefully, there's also some kind of ball hanging from a string that's tied to the platform holding the cup of tea. The ball continues to point toward the belly of the plane, even when the belly of the plane is pointed toward the sky.

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What is the difference between a conventional and an RNAV holding?
While reading in the PANS-OPS (Doc 8168-OPS/611 Volume II) about holding procedures, I came across Chapter 7 of Part III section 3 defining RNAV holding procedures and differentiates them from conventional ones described at an earlier section. Under 7.1.3 is mentioned that

Location and number of holding patterns [...] The normal location would be at one of the IAFs. RNAV holding waypoints shall be located so that they are referenced to and verifiable from specified radio navigation facilities. The holding waypoint (MAHF) is a fly-over waypoint.

At that point I recalled the GNSS RNAV procedure from BEDEX for LGKR airport. There we can see that note #2 warns us that the holding is a conventional one. But why can't it be treated as an RNAV? It's on the IAF, it's defined by KRK VOR/DME (thus verifiable and from specified radio navigation facilities), even the path to MAHF (Missed approach holding fix) seems to be a fly over.
The rest of the chapter is defining the geometry protected areas etc that from the description I would expect them to be smaller than that of the conventional holding pattern:

Aircraft equipped with RNAV systems have the flexibility to hold on tracks which are defined by the RNAV equipment and to use procedures which are less rigid than those used in conventional holdings. The benefits of using this technique include the optimum utilization of airspace with regard to the siting and alignment of holding areas as well as, under certain circumstances, a reduction of holding area airspace.

So what makes conventional holdings "incompatible" to RNAV?

A conventional hold based on legacy radio-navigation required overflying the hold fix on entry as guidance is only available inbound to the fix and your exact position is known at the fix (with some allowance when inbound if there's a DME at the holding fix.) Hold entries from the holding side of the inbound leg will result in crossing to the non-holding side of the inbound course and thus require protected airspace on the non-holding side. The outbound leg of the hold is normally defined by time based on published holding airspeed. Protected airspace has to allow for wind factors and the limited navigation accuracy when flying the hold.
With an RNP capable FMS or GNSS-based navigator, the path of the racetrack can be defined and flown with guidance throughout the hold (including entry and exit.) As a result the Minimum Aviation System Performance Standards:
Required Navigation Performance for Area Navigation (RNP MASPS, RTCA DO-236) require containment within the maximum size holding pattern defined in the MASPS. The key differences are entries are not required to overfly the fix (fly-by is allowed) when entering from the hold side to avoid crossing to the non-hold side. Entries from the non-hold side (teardrop and some direct entries) typically will overfly the fix. Once the aircraft has entered the hold it is expected to fly the hold as specified until it exits. Exits can be either fly-over or fly-by the holding fix as published.
The biggest change is in a parallel entry. Entry is a fly-by the hold fix to fly outbound on the inbound course, followed by a 225 deg/45 deg reversal on the holding side to join the inbound course and cross the fix to be established in the hold.
Direct entry from the hold side results in the initial outbound turn extending further past the hold fix as a result of the initial fly-by at the hold fix. The aircraft is then established in the hold when it joins the outbound leg.
Since the RNP nav system can provide path definition of the hold and guidance the total protected airspace can be reduced when compared to the conventional hold.
Conventional holds are not in general incompatible with RNP holds. An RNP capable FMS will treat all holds as RNP holds. The only issue I see here is the comment: DEFINED BY USE OF KRK VOR/DME. That would indicate to me there is an inconsistency between the VOR/DME computed positions and the fix positions contained in the database.

The FMS database itself is not the issue. A hold in the database (or when created by the pilot-you can create a hold anywhere) is defined by 1. the hold fix, 2. the inbound course to the fix, 3, turn direction, 4. leg length (time or distance.)  That's it.  The FMS I worked on treats all holds the same and generates an RNP path.  The only thing I can see that would be an issue with this is the second part of the note: DEFINED BY USE OF KRK VOR/DME. If there's an issue with the KRK position or orientation, a database generated position of the fix would be off.

@Gerry Thanks for the update! That note is still a bit weird (I don't think there is a position inconsistency, how else would you fly the hold in an aircraft which is unable to track a VOR, like the A320?). My Jeppesen chart doesn't include that note, it only says "... join conventional holding at BEDEX..." in the missed approach description.

@ymb1 It is all a bit confusing. I doubt A-RNP is the issue as it is fairly recent and not in widespread use (FAA has it as optional) and it's not likely to have a major impact on the FMS which only defines the path. RNP is set in the database. In Doc 8168 there are some unique requirements for VOR/DME holds with optional entry procedures which are not implemented in the FMS IIRC. That may be the issue. BTW, one entry description looks like A350 entry you were seeing on FlightAware.

Gerry excellent addition! Could that mean that KRK might need recalibratarion/flight testing in order to provide accurate fixes? Magnetic variation changed recently, runways had to be re-numbered. @Bianfable the A320 unable to track a VOR? How's that possible? (although I'm afraid I have to ask a new question.) PS: I am trying to get ahold of the office who designed the procedure, though I'm not sure if and when will that happen.

@SteliosAdamantidis Airbus removed that possibility with the A320. Feel free to ask a new question...

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How are runway changes performed when radar vectoring is available?
When the time comes to make a runway change, let's say because wind has changed direction, how is this performed?

Aircraft might already be on finals, what does ATC do? Do they ask them if they want to continue with the approach or be vectored to another runway?
Aircraft might not be on finals but being vectored to the finals. Same question here.
Finally, there might be aircraft on the ground already taxied to the runway. Do they takeoff anyway or do they taxi to the new runway?

Related: How does a large airport switch flow?

@mins That pretty much answers the question. But what can be done so that if someone else interested comes across the question? As far as I know "runway change" is close to the terminology while "flow switching" is not. I bet that if I delete this one, there might be someone else asking the same after a while...

@steliosAdamantidis Technically, flow change/switch is what you're talking about in this question, a runway change is literally changing a runway an aircraft is assigned to. So a simple change from the Left to the Right is a runway change, changing from 35L/R to 17L/R is a flow change, or changing the active runways. Though technically a flow change is a subset of runway changes.

You don't have to delete your question, it's a good question which happens to be already answered. If you don't delete it, it will be marked as duplicate and the other URL will be included in the duplicate note. People reaching your question in their search will continue to the other by clicking the link. If you want to delete it, you may do so indeed.

@mins That sounds good.

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Why do aircraft on FlightRadar24 jump around randomly sometimes?
I use FlightRadar24 on my iPad to track friends'/family's flights when they are traveling (not paranoia, just curious).  I've noticed that, quite often, their plane will jump from one location to another, or jump backwards down the flight path, or zoom forward, or any other number of motions that I assume the plane isn't actually making.  (My personal favorite being when they miss the runway on touchdown and the plane disappears.  If that actually happened as often as Flight Radar 24 made it look like it was happening...)
What makes the planes do this on FlightRadar24?  Why can't it just track the planes correctly?

FR24 relies for most of the tracks on ADS-B data. Part of the ADS-B transmissions is the position. There are three causes of the behaviour that you observe:
1). Aircraft landing next to the runway
The position source onboard the aircraft is not always GPS. Mainly older aircraft (e.g. Fokker 100) have their Inertial Navigation System (INS) coupled to the ADS-B transmitter. The INS relies not on external radio measurements but only on measured acceleration and rotation to track its position. It is usually correct at take-off, but it develops biases over time and therefore the landing appears quite often next to the runway. I can assure you that this is mostly misleading.
2). Short time track offset
In most aircraft the ADS-B position is from GPS. When the GPS loses its  position fix, the system falls back to INS. As described above, the INS position is slowing drifting from the truth during the flight, so the ADS-B track will shortly jump aside to the INS position until the GPS comes back. When short (e.g. 1 position update) the offsets appear as spikes.

3). Long distance jumps (180 NM, 360 NM)
Due to the limited number of bits available in the ADS-B messages, position is encoded in a complex format called Compact Position Reporting. It requires at least two position messages to decode the first position of a track, from that point onward, every message will constitute a position update. When no proper verification algorithms are used in the software, it may occur that a receiver station initializes the track wrongly, usually causing a jump of 180 or 360 NM.
Also note: When INS is used a the position source, the ADS-B data contains an indication that the data is not to be trusted, but that is silently ignored by FR24.

For aircraft that do not transmit their position over ADS-B, but have a Mode-S transponder on-board, FR24 multilaterates their position. This is a process relying on the difference in travel time of the radio signal from the transponder to several receivers. Based on the time difference of arrival of the same transmission at various location, the position of the transmitter can be calculated. This works only if three or more receiver receive the signal.
Since radio waves, as a form of electromagnetic radiation like light, travel at the speed of light, the clocks in the receivers have to very precisely synchronised to determine the difference in arrival time of the signal. A microsecond deviation can already cause a position error of several hundreds of meters. Due to this, Multilateration tracks in FR24 are often a bit jagged.

Could you possibly edit the question to explain what an Inertial Navigation System actually is?  I'm not sure why it would be so different from GPS.

@JayCarr INS is topic on itself, quite complicated. Instead of relying on radio signals like GPS, it relies on measuring accelerations and rotations to keep track of position. Feel free to ask another question and I am sure someone can provide a good explanation. (or else I'll try)

Oh, I probably will.  I was more hoping for that one line answer that you put in your reply right there.  Just a primer for people (like me) who have no clue what-so-ever and want a one line clarifier.

@DeltaLima - Excellent, exactly what I was looking for on INS (for this answer).

@JayCarr your welcome, thanks for helping me to improve my answer.

An additional reason: sometimes the aircraft will pass out of ADS-B range, as it relies on receivers on the ground. This tends not to happen over Europe much, and the USA is pretty good, but around Africa then the lack of or spotty signal can make strange things appear to happen.

Not to take away from already great answer provided.  In my experience the jumping behavior you are describing in Flightradar24 is due to MLAT triangulation that is used to establish approximate location rather than absolute (using GPS).
Older planes transmit a SUBSET of ads-b data, which does not include aircraft location.  So FR24 knows that there is an aircraft in the air, but doesn't know its location.  This is where multilateration (triangulation really) comes into play.
If you have a few (minimum of 4) receivers available AROUND the aircraft that are tuned precisely to the same clock, you can measure how long that same ads-b signal reaches all 4 receivers from which approximate location can be determined.
In FR24 you can verify which of the "jumpy" planes are being tracked by MLAT setup by looking at "radar" that is tracking it.  If MLAT is used you will see "T-MLAT" as the source.
If you indeed see jumpy behavior on the planes that are tracked by "T-###" or "F-###" sources then I would agree with already posted answer by DeltaLima

Sometimes I wish we could combine answers on this site, just so that if two people have parts of the answer I could mark both as correct...

No worries Jay, it's all about learning, we are all learning from all these different answers, that's what this community is about!

Re: INS - Since there are no ground based radio transmission navigation stations in the ocean (VOR's or ADF's), the INS (inertial navigation system) was designed to help jets navigate safely over the ocean (before GPS).  INS uses a series of gyroscopes and accelerometers to measure how far a plane has traveled from a specific point.  With multiple accelerometers it's able to figure if the plane turned to a specific heading and how far it's gone (it can do this through multiple turns and speed changes).  To set the airplanes INS, a pilot pulls up to a specific INS set point at an airport and calibrates it (before the trip).  INS is so accurate that it typically holds a planes position to within a few miles after traveling 2500 miles.  The INS system can also be set from a GPS.  The major advantage to INS is it doesn't rely on any external signal to work.

The answers you have been given accurately describe why a historical flight's track may have discontinuities or errors. Those answers apply to any flight tracking website which depends on ADS-B or multilateration technology to determine an aircraft's location.
But to answer your specific question about live flights displayed on FlightRadar24:

I've noticed that, quite often, their plane will jump from one location to another, or jump backwards down the flight path, or zoom forward, or any other number of motions that I assume the plane isn't actually making. ... What makes the planes do this on Flight Radar 24?

FlightRadar24, unlike most other tracking websites, attempts to display a literally real-time indication of an aircraft's location.
This means that when it receives a position report from an aircraft's ADS-B, or a multilateration report from multiple ground receivers zeroing in on the aircraft's location in space, it does not only display that point. Rather, it displays that point and then goes on to "push" the aircraft's icon farther along its predicted route based on the previously reported points, which combine to describe the aircraft's track and groundspeed.
(ATC radar displays will also do this: if no update is received on a track, it will continue to "coast" for a few seconds on its last known course and at its last known groundspeed. Eventually the target will re-acquire or the track will be removed from the display.)
When FR24 next receives a position report on the aircraft, it plots that point on the map and updates the prediction. If the position report is in line with the previous prediction you will not notice much change. But if the aircraft's reported or detected position is changing (whether due to tracking and reporting inaccuracies, or because the aircraft is actually changing course or speed) then there will be an obvious retroactive "jump" forward, side-to-side, or even backward.

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A380 reverse thrust on only half the engines
I noticed on this video of an A380 landing in rain that reverse thrust was applied to only the inboard engines. Do the outboard engines not have reverse thrusters? If they don't, then why not? If they do, then why not use them on a slippery landing?

IIRC they do not have trust reversers on the outside engines, as the engines are far away from the centerline. This means that the force of the thrust reversers would place a very large bending moment on the wing, which would require stronger (and heavier) wings

@ROIMaison: Thank you. You might want to post that as an answer so that I could accept it!

The thing is that I'm not sure if this correct (and if this is the only reason) I'd prefer backing if up with resources before posting it as an answer :)

@ROIMaison: The bending moment is not the problem - if the regular thrust can be transferred, reverse thrust can be as well. FOD is the problem.

@Peter, is this true? I can image that structures are designed for a certain load (not only a certain force, but also a direction), and I'm not sure if this also means that the structure is as strong in the opposite direction

@ROIMaison: Aluminium and Carbonfiber are almost as good in compression as in tension, so the direction of the load is secondary. This is not true if buckling stiffness is not sufficient, but in case of wing in-plane bending, buckling is of no concern.

@vasin1987: I agree about the dupe status. Thanks.

@dotancohen you're welcome :) feel free to ask more question!

Yes, the outboard engines do not have reverse thrust to avoid them kicking up dirt. On a regular runway they will be outside of the concrete surface, so using reverse thrust there will incur the risk of foreign object damage.
This was already covered in this answer.

Thanks Peter! Apparently Google still has some work to do indexing this SE site!

@dotancohen: I found it only because I remembered it, but I have to say the SE search is doing a nice job (when you use the right search term).

You are right, I should use the in-site search too. Thank you!

Why can't the pilot(s) just avoid using reverse thrust on the outboard engines while they are over an unimproved surface?

@SpongeBob: Including a thrust reverser would add weight to an aircraft that is already 5.5 tons over the promised empty weight. Initially, no thrust reverser was planned, and the inboard ones were added late in the project. Nobody felt the need to add outboard ones, too.


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Why not mount airliner jet engines above the wings?
It seems that most airliners put the engines below the wings, i.e. the Boeing 7*7 series and the Airbus A3** series. This requires long (heavy) landing gear, and the engines are close to the ground which may cause damage to the engines (ingest debris) or the ground.

Why not mount the engines above the wings? In addition to the shorter (lighter, stronger) landing gear, the plane would be easier to service and embark / disembark. What are the major disadvantages to having the engines above the wings for civilian airliners?
The question "How does the mounting location of a jet engine affect aircraft performance?" addresses the performance issues affecting engine placement but answers do not cover over-wing placement extensively and focus only on performance and not other operational issues or design advantages.

Note that low-wing turboprops do have engines mounted on the wing.

The Honda HA-420 HondaJet has its engines mounted above the wings.

Have a read of this answer for some info: http://aviation.stackexchange.com/a/1470/59

@RoryAlsop, RedGrittyBrick: Notice that I link to that thread in the body of the question!

I've edited the question in the light of comments and to somewhat address the aspects that made it look to me like a potential duplicate. Please rollback my edits if you feel it changes the nature or content of the question too much.

@RedGrittyBrick: Thanks. I believe that the edit narrows the scope of the question, but knowing the folks here we'll get a treatise with engineering diagrams anyway!

Honda has discussed this design thoroughly.

http://aviationweek.com/site-files/aviationweek.com/files/archive/www.aviationweek.com/Portals/AWeek/TWW/Boeing%20BWB%20STV.jpg

While it's true that shorter landing gear weighs less and is easier to find space to stow when retracted, it's actually not really stronger per se. Having longer shock absorbers in the landing gear makes them able to deal with larger landing weights, as longer shocks that can travel further don't have to produce as much momentary force to yield the same amount of work.

@Thank you reirab. I had considered that, but notice that the engines under the wings determine the minimum, i.e. fully compressed, gear length. Thus, requiring longer gear due to clearance issues does not increase the amount of room for shock absorbers to function.

Another disadvantage not mentioned in answers is that the flow out of a jet engine is very hot, and special materials are required to withstand the heat.

@reirab note gear design of F4U http://en.wikipedia.org/wiki/Vought_F4U_Corsair#Landing_gear_and_wings

Another plane worth mentioning is the Antonov An-74 which also has the engines mounted over the wings but being a plane with wings fixed atop of the airframe, it wouldn't have the noise and visibility problems for passengers. This design also has other advantage (cf. Coandă effect).

Is this a real photo? (The cargo crate in the engine intake)

@RoboKaren: Yes, that is a real photo. Luckily that wasn't a Boeing 777 instead.

Maintenance
Having the engines below the wing makes them fairly easy to access, even if some kind of lift is needed. Putting them above the wing would make them much harder to get to. Dropped a tool? Better start on that wing repair too. This includes both general access to the engine and the procedures for removing and installing the engine.
Structure
An engine below the wing is fairly stable, since it is hanging from above. It naturally wants to keep hanging downwards. Mounting the engine above the wing would be less stable. It naturally wants to tip over.
Noise
If an engine is under the wing, it helps to block some of the noise from at least the mid cabin. An engine above the wing would expose much more of the cabin to noise. It could reduce the ground noise while in flight, though.
Aerodynamics
The top of the wing is the most sensitive part aerodynamically. This is why items like fuel tank access panels are placed on the bottom. Having an engine and pylon on top would affect the flow over the top of the wing.
Safety
Engines falling off the wings tends to be a bad thing. But if they were above the wing, they would tend to fall down onto the wing, which would still not be good. It would be harder to have then break away in a crash. Also, in the event of an uncontained failure, the wing would not provide any protection to the fuselage.

Of course there are benefits, such as the reduced noise, less ground clearance required, no interference between the jet blast and the flaps, and less chance of FOD being ingested. As new engines get larger fan diameters, the constraints become more difficult. Some concepts of the blended wing body design put the engines on top of the body. But for the current design of aircraft, the benefits of having the engines below the wing are greater than those of the alternatives.

Disagree with Maintenance: Big-airplane shops have all kinds of lifts, access would be a non-issue. Ramp access would be harder though. Engine swap would be easier as you can use a crane rather than squeezing everything underneath.

Disagree with Aerodynamics. Fuel tank access is on the bottom because it's more convenient for the ramp crew. Plenty of low-wing aircraft have the fillers on top. With the cover closed it doesn't make any difference. The rest is simple engineering.

Disagree with Safety: Engines don't fall off much anymore, and one that did (Flt. AA191 in 1979) had the engine flip OVER the wing. Installing it with a crane would probably have prevented the accident altogether.

@paul Disagree with your disagree with maintenance. It's much easier to have an engine on a cradle and jack up the cradle to lift the engine under the wing than it is to have the engine dangling from a crane.

@paul another disagree with your disagree with maintenance. With underwing engine, a technician can carry out minor maintenance (and also, inspection) from the shop floor. Ok he may need a step or platform, but it's better than having to keep climbing on the wing for every little minor task. Also imagine the shock commercial passengers would have if they saw a tecnician climb on the wing at the airport gate to check a minor problem like a spurious warning indicator. With underwing they don't even realise anything's happening.

Yeah, ramp maintenance will be less convenient like I said. But if your shop has an overhead crane it will be easier to handle large engines from above. Picture the extra access you will have to all the parts when the engine is suspended from 2 lift points on top rather than having to share floor space with the cradle. For the passengers, print "Don't Panic!" on the back of the coveralls :-p

@Emrakul Disagree with your disagree with structure. :) If the pylon is holding the engine on from the top, gravity will dampen any lateral motion. If the pylon is holding the engine on from the bottom, gravity will naturally exacerbate any lateral motion.

Agree with maintenance - the RAF specifically complained about having to use cranes to get at Nimrod engines rather than jacks. Agree with aerodynamics - I've seen simulations directly comparing below wing pod, above wing pods and conformal tanks. ( I used to be software technical authority for BAE's mathematical computing dept )

On aerodynamics — over the top engine can be used to purposely improve it by blowing exhaust over wing surface. The prominent example is Antonov An-72, however as I was told it was such a hell to develop and get right, that no one bothered to go there after.

But putting the engine above and in front of wings would allow employing Coanda effect, right?

There was one design with overwing engines: The VFW-614. The number was chosen because it was the 4th project to be started in 1961 by the Vereinigte Flugzeugwerke (VFW).

The engine placement had several advantages:

less risk of ingesting foreign objects
less noise during take-off and landing, at least for the people on the ground
smaller trim change with power changes

But the disadvantages (cabin noise and engine access) were the reason why this engine placement never took off. Also, low engines can get their fuel without pumps, just by gravity. However, pilots who flew both the 614 and the Boeing 737 told me that the 614 was more pleasant to fly since it needed no trim changes when the power setting was changed.
Placing the engine forward of the wing helps to dampen flutter, but then the main advantage of overwing placement, reduced noise footprint, is lost. Todays engines are mostly placed ahead of the wing for that reason, and below it so they are out of view for the passengers but easy to reach for maintenance crews. Placing the engine directly under the wing would help with feeding it pre-compressed air, but again the forward location makes little difference in terms of precompression but helps with flutter damping.

"never took off".  heh.

the 614 was more pleasant to fly since it needed little trim changes during the whole flight.  Do you mean it needed few trim changes during the whole flight?  As written, this looks like "it needed little (minor) adjustments repeatedly throughout the flight," which I would imagine would make it less pleasant to fly.

@MasonWheeler: I hoped the context would help, but I agree that the choice of words was not good. It should be clearer now.

Yeah, flying on without needing to change most of the time means few changes, or less changes (compared to the other way).

"so they are out of view for the passengers " -- surely this is not really a factor  in the design of the aircraft-- ??

Or, to protect the manufacturer's reputation in case they catch on fire or otherwise self-destruct?

If we ignore the other engine placement options considered in the linked question, we can compare only over vs underwing placement. I'm no expert but here are some factors that occur to me:

Underwing simplifies engine access, the engine is close to the ground. Since most engines are mounted this way it may be that engine-designers optimize placement of components with this in mind (though engines are often produced for a specific plane)
Underwing mounting means that gravity helps hold the engine in position laterally. For overwing placement, the opposite is true and you might need a slightly stronger pylon and wing-spars?
Overwing placement causes the torque on the wing from the weight of the engine to act in the same direction as the torque from thrust, underwing location reduces total torque - though this may not be significant.
Engines are at maximum thrust at take-off. An overwing engine at maximum thrust would probably be more likely to exert a torque on the airframe that opposes lifting the nose for take off. I'm not sure if this is good or bad but it seems wrongish.
Overwing placement certainly decreases the risk of FOD but may impede passengers view and increase noise.
Aircraft landing gear may have to be a certain height anyway to keep the tail clear of the runway during take-off rotation and to absorb landing forces over a longer distance. This may not be significant as there are large aircraft with very short landing gear (e.g. some military and civilian transport aircraft). Perhaps they pay a penalty for this.
There are probably more airliners than large airports, so it may be thought better to remove FO from runways than make general airliners more FOD-proof.

 source: Bartosch

Good point about the torque, I hadn't though of that.

A caption on the photo would be helpful. Was all that debris from an engine, from runway cleanup, or what?

@Carey: It seems to be typical of a 15 minute sweep of an airside stand/gate. See test results.

I painted the new pictures myself but took the text from an external source:

You can see with the engine mounted over the wing, you have the
  centerline of thrust located above the longitudinal axis of the
  aircraft. This creates a nose-down pitching moment about the lateral
  axis, which is at the center of gravity (CG). While the weight of the
  engine does help counteract it, it must also be countered by an
  increased amount of downward lift created by the horizontal stab (a
  greater tail-down moment).

On what basis is the center of mass determined in these photos? In the second photo, it seems way too low to my eye. Though my only experience is with KSP.

I will answer only for the landing gear length. When you consider large enough aircraft, you need a long landing gear to reduce the risk of tail strike when landing and taking off. Thus, you have enough place underwing.
For example compare the length of the nose landing gear of an aircraft whose engines are mounted underwing (e.g. this A320) with the one of an aircraft whose engines are not mounted underwing (e.g. this Caravelle). I choose photos with a man near to the landing gear to ease comparison.

How about the B737? That plane is about the same size as the A320 and has underwing engines, yet has extraordinarily short landing gear.

@dotancohen according to the answers of this question, the distance between the ground and the aircraft is not that different for those 2 aircrafts.

Thank you, that questions references another question which links to the airliners.net photos that helped prompt this question! I'll take a look comparing the engine ground clearance and the landing gear length, thank you.

@ManuH Unfortunately, your links return error 404. :(

Looking at those two photos, the Caravelle's nose gear looks appreciably shorter than the A320's.

There is one very good reason to put engines just above the wing, as seen here on the NASA QSRA:

and the YC-14:

This is known as "upper surface blowing", or some variation on that theme. The idea is that the airflow from the engine follows the upper surface of the wing, so when the flaps are lowered the airflow follows their smooth bend until they are blowing downwards, which greatly increases lift. This is an alternative to lower surface blowing seen on the C-13:

and it's much larger sister, the C-17:

The USB solution has a number of major advantages over the LSB. The main one is that the airflow doesn't blow directly onto the flaps, which makes the structural loads much simpler. The airflow is also greatly smoothed out by its flow over the top surface of the wing, which also lowers loads. Finally, since the flaps are already accelerating airflow over their top surface - pretty much the whole idea - the overall design is actually far simpler. The end result is the same, both improve lift by bending the airflow downward via the flaps, but USB was mechanically much simpler and this was a major selling point for the C-14.
So... why didn't they use it? Well, ironically, one of the reasons is that it was too good. In the case of an engine-out, especially on the two-engine variety, one whole wing would lose lift and it was practically impossible to keep control. A four-engine variety addressed this, but the original program wasn't considering those and Boeing was pushing the two-engine layout as a major advantage (in maint terms). In contrast, the LSB models had less lift augmentation and had to rely on "more flaps!" to get the same performance (which, IIRC, they never did), but as a result they had better response in an engine-out condition.
It is not clear to me that the C-17 ended up with LSB for any reason other than that it came from McD, and that had anyone else won the contest they might have used USB.

Placing turbines in underwing pylons began with early US jet bombers, the B47 and B52, and the C135 transport - later to morph into the 707. In his book 747, Joe Sutter (the lead engineer on the 747) gave the reasons for underwing pylons rather than the in-wing engine placement that was used on other early large jets like the Comet, Victor, and TU-16, as:

Maintenance
Less damage in the case of catastrophic engine failure (early
turbines weren't as reliable as they are today) or fire.

As to why over wing pylon placement isn't used... both reasons still apply.
Most maintenance on turbines is done on the aircraft - engine removal is not common, so the lower placement facilitates quicker average maintenance. Engine removal/replacement is facilitated with a forklift.
Catastrophic failure or fire... quite rare, but when it happens, the engine will normally drop off, away from the wing.
Also, under METO, the lower engine placement, under the CG, tends to pull the nose of the plane up rather than down, which is what one wants on takeoff or most situations where a pilot applies full power. Over wing placement would tend to pull the nose down on takeoff. A minor factor, but worth mentioning... no point in taxing the elevators more than necessary on takeoff, when control authority isn't the greatest due to minimal airspeed.
One rare exception to underwing pylon placement protecting the wing was AA Flight 191, the Chicago crash. Due to poor maintenance techniques, the rear engine mount on #1 broke, the engine pivoted upward, broke off, and went over and into the left wing, tearing out the hydraulics for the front spoilers. The pilots thought they were dealing with a simple engine failure, and followed the book for climb out with a single engine failure, maintaining an airspeed consistent with takeoff flaps set on both wings. Due to loss of lift from the damaged wing, the left wing stalled, and the aircraft rolled left into the ground. Not enough altitude to recover.
Having said that, this sort of catastrophic failure is quite rare, the most recent example being Qantas 32, an A380 that suffered a major inflight engine explosion. The engine did not drop off of the aircraft, and it was able to land safely, albeit with some degradation to control authority of the ailerons. Whether or not over wing placement would have resulted in more damage to the critical upper wing surfaces is a matter of conjecture.
One recent executive jet noted for over wing engine placement is the Hondajet. They include a short passage on the advantages:
A breakthrough in aeronautics, the Over-The-Wing Engine Mount was engineered and proven by Honda after more than 20 years of extensive research and development. This innovative technology not only breaks the conventional mold set by the aerospace industry, but also provides category-leading advancements such as a more spacious cabin, noise reduction, and increased fuel efficiency.

Another thing that has been partially mentioned. The pylons holding the engines are designed to break before any extreme vibration or unbalanced load (due to a failed fan) causes severe structural damage to the wing. Underwing placement means the engine won't fall down onto the wing and should have plenty of clearance for the horizontal tail. Over wing placement would or could result in impact with the wing and horizontal tail or even with the fuselage if the bank angle was severe enough.
In addition having the thrust line above the wing would create a nose down torque along the wings axis which would be compounded by the pitching moment developed by the airfoil. This additional moment would require stiffer and therefore heavier wings.

Regarding engines breaking away cleanly, El Al Flight 1862 shows that while that may very well be the intention, it's not always the case in practice. In that particular case, engine 3 (right wing inboard) detached and ultimately struck engine 4 (right wing outboard) causing both to separate from the wing (along with significant damage to the wing itself).

Thanks for the insight. I guess that situation reinforces the statement that you can't plan for everything.

Below the wing helps lift.
Above the wing hinders lift.
Below allows the air to go over the wing not spoiling the aerodynamics for lift.  Above disturbs the aerodynamics for lift, depending how far back the engine is on the wing. Sure lighter landing gear is good, aircrafts don't use the landing gear when flying, and besides the engines weigh far more then the landing gear. It's better to have the engine under the wing. New models can raise the wings and can decrease the pylon length. However the lift is not yet enough. They need lift, every heavy cargo aircraft has the engines under the wing. They cannot afford to lose any possible lift.

Welcome to aviation.SE. your answer is hard to follow. If you present several arguments, you may put them into separeted paragraphs. Moreover, you should add links and references and highlight how your (late)answer add new elements. You may also read the help center.

Below the wing hinders lift (in most cases). Lift is generated by increased air speed on top, increasing the speed on the bottom, which an engine does, lowers the differential and thus lowers lift.


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How does an aircraft designer increase dynamic stability?
This question explains that an aircraft can be statically stable (it will seek to return to equilibrium) but dynamically unstable (the amplitude of the oscillations increase) if there isn't enough damping in the stability equation.
That's fine from a mathematical point of view, but what practical change would increase the damping and dynamic stability?
I've seen quite a few radio-control trainers that are dynamically unstable, and would love to know how to fix the problem so that they're easier for the student pilot to fly.
These planes typically pull out of a dive on their own, but then climb excessively and stall, leading to another dive. Each subsequent stall and dive is more dramatic than the last.

The old saw is to move weight forward.  The ASE explanation generally involves torque around the CG.  Keeping wing CP aft of CG would help control rise of nose as lift increases (because the wing actually torque the nose down). Additionally, more of the wing now functions as a "tail" (stabilizing area behind the CG).  From work with model gliders, essentially the wing is too large/strong for its "tail".  One must be wary of excessive stability, which makes it harder to pull out of a dive.

@RobertDiGiovanni - Isn't that just static stability? I'm talking about planes that pull out of dive on their own, but then climb excessively and stall, leading to another dive.

Not really, it depends whether or not the wing is lifting the nose or the tail is pushing down.  I can see how swept wings really drive engineers batty, particularly when slats are deployed. Moving CP too far can make control difficult, especially with a smaller tail.

@RobertDiGiovanni - Can you explain how that is different from static stability?

I've seen in claimed that moving the CG forward can actually make dynamic instability worse, because more decalage (download on tail) is needed.  I don't know the truth of that.  A good place to seek further discussion would be this on-line forum -- https://www.rcgroups.com/modeling-science-136/

@Robin Bennett the difference is that both seek the original flight path, dynamicly unstable increasingly overshoot it (a little like Dutch Roll in pitch).  Again with swept wings, tips deteriorate first when higher AOA is reached, adding to nose up forces (if wing is lifting the nose)  quiet flyers point is also valid, but excessive differential of CP and CG is the root cause.  Notice how how slats deployed might make it harder to pull out of dive (with swept wings and forward CG).

@quiet flyer your suggestion to open spoilers is interesting as it "weakens" the wing a bit.  Dropping gear would lower CG and center of drag (canceling pitch effect), but Bob Hoover liked it for spins.

If you're talking about R/C airplanes, aerodynamics per se, is fine, but what comes to my minds eye are scale issues like (i) power/thrust to weight ratio for these R/C trainers surely affect how they fly, and the way they have to be flown, (ii) being small and lightweight, the destabilizing factors such as wind gusts could typically engulf the whole airplane. (iii) speed to size ratio? A 170ft long fuselage travels 3 fuselage lengths per sec at 300kts (507fps) whereas a 3ft long R/C model at 60kts(101fps) is already 33 fuselage lengths per sec.  Are these factors relevant enough?

@skipper44 no they are not. Books could be written about the subject, but there are similarities even in scale.  There is a relationship of tail torque and wing torque.  Speed control is critical (look at quiet flyers suggestion to drop gear and use spoilers).  You would help yourself as an engineer to look for similarities throughout scale.  But I would agree that the question could be more specific to one type of aircraft.

@RobertDiGiovanni - If you want a specific aircraft, the Multiplex EasyStar is a good example. It was the most popular electric trainer for years and has been widely copied. It's easy to make statically stable, but usually dynamically unstable.

@Robin Bennett  Yes, that one will require downtrim as speed increases, much like a 172 going into cruise.  Note that downthrust helps some, but, like most models, it may be a bit overpowered.  Many novice modelers fly (and land) way too fast.  Interesting in that the discussion is leading to speed V = thrust - drag, and lift is proportional to V$^2$!.  I might try that plane.  Thanks.

It the plane pitches up until it stalls, it is statically unstable (if the CoG is behind neutral point, but still ahead of midchord, the plane becomes stable in stall and pitches down, which allows repeating the cycle). In dynamic instability the plane flies up and down, but the angle of attack remains fairly constant, so it should result in a sine wave growing in amplitude with tops just as smooth as the bottoms.

@Jan Hudec "flies up and down, but AOA remains constant" would imply changes in velocity (less static stability).  There is also a short period oscillation, where increasing wing lift tries to pull into a loop (increasing AoA of downlifting tail faster than the stabilizing forces (tail, aft fuselage area) can stop it).  These two aspects make it interesting and delightfully confusing.

@RobertDiGiovanni, it implies changes in velocity, but that says nothing about static stability, only about a lack of damping, that is dynamic stability.

Damping is produced by drag and by large induced speeds at the tail surfaces from a given disturbance. This can be caused by long lever arms of these surfaces or by high air density.
More on the topic can be found here:

What is aerodynamic damping?
Will control surfaces on a plane be less efficient at a higher altitude?. The lower density at high altitude reduces the vertical or sideways speed component caused by a rotation relative to flight speed, thus reducing dynamic stability.
Another trick is to use a conventional tail instead of a V-tail, as discussed here.
What also helps is to shift the eigenfrequencies of the plane away from the response delay of the pilot in order to avoid PIOs. An unusual example would be the Wright Flyer.

These planes typically pull out of a dive on their own, but then climb excessively and stall …

This is the classic long period mode in longitudinal stability. Since rotation rates are low, pitch damping also is low and the most important damping contribution is from drag. A low L/D reduces the tendency to overshoot, a high trim speed reduces the tendency to stall (and shifts the motion to higher speeds with lower L/D). Reducing static stability will make the period longer such that it becomes easier for the pilot to react. However, lower stability will make the pitch response more sensitive which increases the risk of too large control inputs.

That certainly matches the planes I've seen. The ones that were dynamically unstable were efficient glider style planes, while basic boxy designs with fixed gear were much more stable. Also, learning to fly in this sort of trainer usually involves the student's response time improving with practice until they no longer have POI - usually only an hour or two of flight time but it would be nice to skip that stage!

You mean Pilot Induced Oscillation?

@skipper44 Yes, that's why I linked to the Wikipedia page for pilot induced oscillation.

@PeterKämpf - you and I both miss-typed PIO as POI

@RobinBennett Thank you for spotting this! Corrected. I wonder how that happened.

@Peter Kampf working with the aviation engineer speak we arrive at: relaxing static stability reduces dynamic instability as a result of large variation in velocity! Indeed common to model aircraft and large airliners alike!

@Robin Bennett so we must choose one or the other with the Multiplex Easy Star.  I might favor static stability and learn to use that trim tab.

These planes typically pull out of a dive on their own, but then climb excessively and stall, leading to another dive.

R/C flying can be started at an early age and gives any potential pilot a huge head start in gaining experience in the all important fundamentals of flight.
A lesson in the importance of keeping CG within the specified range (and the consequences of not) is better learned at model, rather than full scale.
Not paying attention to aft CG limits (weight too far back) will reduce directional stability in pitch and yaw.  It will roll 360 beautifully, but only because the tail will constantly try to drop throughout the roll, always raising the nose. In general the aircraft will be more maneuverable, but harder to control. (This is why modern military aircraft use computers to assist stability).
Among the plethora of bad things (such as stalling low and slow) that can happen, dynamic instability is another consequence of out of range CG.  Especially with models, a fraction of an inch can matter.
But if you build from scratch, it is important to properly match the tail and wing.  Amazingly, a horizontal "stabilizer" destabilizes pitch when a plane rises or sinks vertically.  This is a very important aspect of static stability.
Rising or sinking vertically is a function of lift.  Therefor, excessive lift can cause a plane to "overshoot" its correction to original flight path.  An extreme example of this is a loop.
So we generally design the wing Center of Pressure to be aft of the Center of Gravity so the torque of the wing lift around the center of gravity helps control the pitching tendency when lift is increased.
The further back the center of gravity, the greater the pitching tendency will be.
For custom scratch builders, a larger tail or longer tail moment is an option, but remember, if the tail supports weight, you are essentially building a bi-plane.


text:
How does radius of a propeller affect its performance?
Let's say we have a conventional two-bladed fixed-pitch propeller. All things being equal, would the same propeller but with half the size -- 50% radius, have 50% of the performance of the first propeller?

Here the area counts, so half the length means a quarter of the thrust. Less if hub losses are included.

@CrossRoads I actually didn't think about the hub at all, but thanks, good point.

Would the propeller hub in the middle be the same size? You did say all things being equal, which I read as "unchanged".
Example, 86" total diameter prop, 12" diameter hub, leaving 2 blades that are (86 -12)/2 = 37" from edge of hub to tip of blade, and 74" of working blade length.
Then you reduce the radius to 43" with same 12" hub, so you have (43 - 12)/2 = 15.5" blade from hub to tip, and 31" of working blade length. 31" is less then 1/2 of 74", so you've lost more than 50%.
Assuming the engine can't spin any faster due to the engine governor limiting the RPMs, you're not getting off the ground.

Short answer. No. In engine test cells, where torque measurement is not a criteria, techs utilize what is called a club propeller. Club props are usually large 4 blade props which would be seen on engines larger than the one being tested. The difference being the club prop has had a significant length of each blade trimmed away. Why? The club prop is very good at absorbing power while generating proportionally much less thrust (Low Efficiency). Hopefully this at least partially addresses your question.

Sorry but I don't really understand your point. I guess you would need to increase the number of blades either if a) the length of your props gets too long that the tip of the blades can go supersonic or b) you need better performance and happy to sacrifice some efficiency or c) you would want more clearance around the prop, so by increasing the number of blades you can reduce the length of each blade. So I'm not totally sure how shorter length on a four-bladed prop answers my question.

I guess that to better understand the question, we need to know what you mean by 50%, ie same prop with blades cut by 50%? Or a prop of 50% scale? same rpm?  different rpm? To what performance metric are you referencing? My answer was floated in order to give the questioner a real world example of a short blade prop for the purpose of intentionally minimizing thrust and absorbing power.


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What if there are no volunteers to sit in the emergency exit row?
I'm currently seated in the emergency exit row, and had an interesting thought. If I was unable or unwilling to assist the crew in an emergency and operate the emergency exit, then I am supposed to contact a flight attendant to be reseated.
But the emergency exit row sucks. The seats don't recline, there's no under-seat storage, there's not even tray tables. What if nobody volunteers to switch seats with me? Will I be rebooked onto a different flight? Or maybe will someone be forced to switch seats with me?
(Let's assume for the purposes of this question that I am physically unable to operate the emergency exit, say because of a broken arm. Let's also assume that the flight is fully booked and there's no empty seat that I could be moved to.)

If everyone refuses to sit in the emergency row, then they start throwing passengers out the plane one by one until they have enough "volunteers".

Note that most exit rows aren't nearly as bad as what you've described. Most of them (in the U.S. at least) do recline, do have under-seat storage, do have tray tables, and have a lot of extra legroom. They're frequently the highest-demand seats in the economy cabin. Being a tall person, when I'm flying in economy, I book exit rows whenever possible.

It's the row in front of the exit row that doesn't recline (because reclining into the exit row would obstruct the exit). The only reason an exit row seat wouldn't recline would be if the row behind is also an exit row.

@TylerDurden actually if you are United, dragging is the preferred method to throwing...

Actually on the flight in question, the exit row didn't recline either.

@RoddyoftheFrozenPeas At least in most cases of non-reclining exit row seats, it's because the row behind it is also an exit row. Over-wing exits often come in pairs, for example. Or sometimes there's a larger door over the wing with a window seat missing from one row, such that the exit can be accessed from either of 2 different rows. In those cases, the forward of the 2 exit rows won't recline. And there are some airlines where no seats recline... At least this is true in the U.S.; some countries have more stringent exit row requirements.


text:
Why would a copilot's window be shaded/covered?
I'm sitting in a small regional airport in Vietnam and I've noticed something odd about the aircraft I've seen arriving and departing. All of these aircraft appear to have the copilot-side window covered or shaded. (The windows are covered from the inside with what looks like the reflective covers you put against your car windshield if you park in the sun to keep the inside of your car from heating up so badly.)
All of these aircraft are ATR 72's, and they're all flown by the same airline. The one I just observed depart had the copilot's side window and cockpit window covered at the time they taxiied to the runway. The one I just saw land had just the side window covered when it taxiied off of the runway and over to the "gate." I can't speak to whether the window was still covered when the plane actually took off since I didn't have a clear view from the airport of the actual runway.
(What I'm calling "copilot-side" is the left-hand side if you're standing in front of and looking towards the tail.)
What is the purpose of keeping some of the cockpit windows covered? Is it a regular practice? (Is it safe? It seems like a safety hazard to cut your visibility in half while taxiing around an airport, even if this place is just an airstrip.)

you wouldn't happen to have a photo or something, would you?

My first thought is - where was the sun shining from?

@Ben - It was early afternoon so the sun was almost directly overhead. When I walked on the tarmac to board the plane, I did notice that plane was facing S-SW direction, so the sun would have been shining into the cockpit from the copilot's side if it were a big lower in the sky.

@Federico - no, sorry. By the time I'd thought to take a photo I was already on the tarmac preparing to board the plane.

Aircraft flight decks can become very warm at times and pilots will always try their best to avoid letting the sun add any additional heat.
Most aircraft have sun visors or sun screens as part of the flight deck equipment. These are usually a clip-on design or pull-shade design. Both types are translucent and can be left in place for all phases of flight.
Many pilots will also bring their own temporary sun shades to use in the flight deck. Theses can be translucent or opaque. Many pilots even use their charts as temporary make-shift shades while parked at a gate in the blaring sun.
Since you described them as reflective covers, I suspect what you saw may have been some kind of temporary shade supplied by the company. They would not be used on the forward windscreen so they would be safe to use during taxiing.
Here are some examples of a pull shade being used in an ATR 72.

Here is an example of what looks like a reflective shade.

Nice answer. BTW what is the vertical lever near the yoke?

That is the hand microphone.


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What qualifies as "open water" with respect to FAR 91.119?
FAR 91.119 governs minimum safe altitudes.  It contains a reference to open water.  What qualifies as open water in the eyes of the FAA?


text:
Why is PCN (Pavement Classification Number) not included in Jeppesen Terminal charts?
Pavement Classification Number goes hand in hand with Aircraft Classification Number (PCN/ACN).
To calculate ACN, it is required for destination airport surfaces such as runway, taxiways & aprons to be of Rigid or Flexible pavement type and PCN number helps to determine whether the aircraft can use the surfaces
Jeppesen Terminal charts has "Taxiway Compatibility" diagram under 10-9B where it says about Codes A to F (wing span & OMGWS (Outer Main Gear Wheel Span)) and nothing about the pavement surface type & its compatibility or under "Airport Briefing" -> "Taxi Procedures".

My questions are:

Should we assume that if for eg. Taxiways are compatible for Code C, then its PCN will be definitely equal to/higher than ACN ?.
Jeppesen Terminal Charts doesn't mention about Runway's & Apron compatibility with Aircraft codes (A to F) or it's PCN. How are we supposed to know whether a stand (under a particular apron) can accommodate certain types of aircraft of a given weight and tyre pressure (PCN) ?.
Where can I find Aerodrome Reference Code (to help determine if the runway can be used by aircraft) ?.


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Can D-ATIS be obtained using D-ATIS Freq. & ACARS DSP?
Can D-ATIS be obtained using and what is the primary difference between

D-ATIS (Frequency given in Airport diagram(jeppesen)) ?.
2.Using AOC function and obtaining D-ATIS using DSP (SITA or ARINC))?.

1.Example: if you look at EDDF (Frankfurt Main) D-ATIS Departure Frequency is 118.730Mhz, should we enter this frequency in RMP3 of Airbus A320 and obtain D-ATIS message using MCDU ?.(I haven't been able to find any videos of pilots obtaining messages using this method)
2.ACARS is a network that is made possible by 2 Major DSP (Datalink Service Provider) SITA and ARINC and Airline partners with either of the 2 to provide them with services, one of them being Weather.
SRC: https://www.youtube.com/shorts/rJOaZ8_2sxQ
SRC: https://www.aviationmatters.co/what-is-acars/ ->DSP Frequencies.
Edit: VHHH (Hong Kong International Airport), Airport Diagram from Jeppesen include D-ATIS frequency and as well as under ACARS: D-ATIS, PDC, DCL can be obtained.
Which one to use to obtain D-ATIS ?.
The advantage of using ACARS D-ATIS rather than using D-ATIS Frequency(From jeppesen chart) is because we can obtain D-ATIS of destination aerodrome before even we are in the VHF coverage of the aerodrome because we will be in contact with frequency(either VHF if flying over ground or SATCOM if flying over oceanic area) of our DSP and DSP will fetch D-ATIS of our Destination.

For a small airport without digital ATIS, the Jeppesen chart will show "ATIS" and the frequency that you tune in a VHF comm radio to hear the ATIS information that was recorded and plays over & over.  You'll hear a controller's voice, reading the winds, temperature, sky cover, active runway, and so forth.
For an airport with digital ATIS, the Jepp chart will show "D-ATIS" and the VHF frequency.  Tune that frequency into a comm radio, and you'll hear a computer voice speaking the ATIS information.  Same info; the notable change is that it's a computer voice rather than a human voice.
If you want to receive the text of that digital ATIS, you'll use ACARS to request it, and if the network connections are all good, then you can get the text of that airport information back as an ACARS message from basically anywhere.  There's no need for any VHF line-of-sight with the destination airport, and they're not transmitting it digitally over any datalink setup anyway.  They're sending it over a network so that it's available via ACARS.
The "D-ATIS" notation on the Jepp chart is there so that pilots can know if the ATIS at that field is available digitally, or if we'll have to wait until we're within range of the VHF comm radio & copy the ATIS manually by listening to it.  It has nothing to do with what's being transmitted from that airport (other than, computer voice vs human voice).
Tuning the published D-ATIS frequency into the VHF-3 radio wouldn't accomplish any good purpose, and would remove the ability for ACARS to use that radio to communicate with the network for all its send/receive functions.

If you check VHHH (Hong Kong Intl) D-ATIS freq for departure is given and also next column says ACARS: D-ATIS,PDC,DCL. If you are saying D-ATIS means you can obtain D-ATIS messages using ACARS, then why mention it separately in 2 different columns and also why have the distinction (D-ATIS Departure and ACARS:D-ATIS) ?.

That next column probably lists everything available for that airport over ACARS, with the decision made to accept the redundancy of stating D-ATIS twice rather than to make that a column of "everything available over ACARS besides Digital ATIS".


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Why are there no protection symbols (=) for high AOA protection on Airbus aircraft?
Green protection symbols (=) are displayed for many protections on Airbus aircraft, such as for bank, pitch, and high speed protection. However, there is no such symbol for high AOA protection. Rather, there are amber and red strips. Why does only this protection use a different symbol, and moreover, why isn't the same concept applied to high speed protection (no protection symbol), when both change significantly with attitude, configuration, and more? In short, why isn't VαMax marked with a protection symbol?
High speed protection:

High AOA protection:

My guess is that because the value where the protection symbol should go isn't normally shown. You can trigger alpha-limit at (almost) any airspeed if combined with just the right pitch command.

High-speed protection is a fixed speed (for example 330kt/M.86 plus 4 knots for A330).
Low-speed protection, on the other hand, is highly dependant on the G-load. If you fly manually and give a pitch input, the yellow/black tape (where the top marks V_ALPHA_PROT) and the red/black tape (where the top marks V_ALPHA_MAX) go up or down. The yellow line (V_LS) stays the same, as that speed varies with altitude and gross weight, not with G-load. This effect is even more pronounced at high altitude.
Therefore, a green mark would give the false impression of a fixed speed, as all the other single markings on the speed tape are fixed speeds (like green dot, S, F, V1, VR).


text:
Approach miniumum when I lost WAAS during approach
I have a GPS receiver with WAAS.
During an LPV approach, I received an LOI message
That means I only lost WAAS, not RAIM.
Did I just need to change minimum to LNAV and continue the approach?

What avionics do you have?

where were you at on the approach when you received the LOI message?  This is my understanding:

Outside the FAF, adjust minimums as necessary for the new procedure (LNAV/VNAV or LNAV) depending on the mode the WAAS GPS fell down to.

Inside the FAF, immediately execute missed approach procedures.

The importance of a stabilized approach cannot be over-emphasized.  If you are below 1,000 FT AGL on an instrument approach and something changes, it is often better to go-around than adjust to the change.  Approach landing accident reduction (ALAR) research confirms the importance of a stabilized approach.
Having to switchfrom a vertically guided descent with a missed approach altitude set in the altitude alerter to a non-vertically guided approach where you must adjust the altitude alterter, and possibly flight director / autopilot modes below stabilized approach alititude could be unsafe in my opinion.

I think the key point here is that this is your opinion. There is no way I would execute a missed just because I lost the capability of following vertical guidance. This is no different than flying an ILS and converting it to a LOC if the glideslope goes out.  When cleared for the approach, you are cleared for all lines of minima.  Also, do you have any links for non-commercial operations and ALAR? I haven’t yet found where this is applicable to either GA or military flying.


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What are the seatbelt rules for pilots and passengers under Part 91?
This is my basic understanding of the FAR's regarding seatbelt rules for civil aircraft:

PIC must brief passengers on how to operate belts (and shoulder harness if installed)
PIC must notify passengers to put on belt (and shoulder harness if installed)
passengers must have belt (and shoulder harness if installed) secured during taxi, takeoff, and landing
PIC (and SIC if there is one) must have belts (and shoulder harness if there is one) secured during the entire flight
shoulder harness does not need to be secured around crew if it interferes with operating the aircraft

Do I have this right?

part 91 operations


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Is the interpretation of "54 knots CAS at the aircraft’s maximum certificated takeoff weight and most critical center of gravity" subjective?
The newly proposed MOSAIC regulations state in § 61.316

(1) A maximum stalling speed or minimum steady flight speed without
the use of lift-enhancing devices (V S1 ) of not more than 45 knots
CAS, except for airplanes, which must have a V S1 speed of not more
than 54 knots CAS at the aircraft's maximum certificated takeoff
weight and most critical center of gravity.

I believe "most critical center of gravity" depends on context of flight condition:
See: Under which condition is a forward CG most critical?
My question to the community: does the text "most critical center of gravity" in the context of the above Notice of proposed rulemaking (NPRM) have an accepted meaning?
Modernization of Special Airworthiness Certification
Am looking for educated answers and less commentary about interpretation.  The (2) fold reason, is:

This assists me in deciding if I should comment on the verbiage with the most informed data I can get.
An example Cessna 182 > D model has a clean stall speed of 54 KCAS when CG is most rearward and 56 when most forward.  Does the above proposed rule clearly indicate in this scenario if this particular Cessna 182 in fact meets the performance limits and design requirements for the aircraft that a sport pilot may operate?

I can't think of anything "most critical center of gravity" could mean in this context except "the center of gravity that gives the highest Vs1." If that isn't your interpretation, then two reasonable people disagree on the meaning of that phrase, and commenting on the verbiage is entirely appropriate!
Under that reading, the Cessna 182 you've given the stall speeds of would not qualify.


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How do I convert my Sudanese ICAO ATPL to UK CAA ATPL?
I have a Sudanese ATPL with an ERJ-145 type-rating and 1858 total hours and 636 hours on type. How do I convert that to a UK ATPL?

The information you're after is all on the caa website here: https://www.caa.co.uk/commercial-industry/pilot-licences/non-uk-licences/third-country-cpl-and-atpl-licence-conversion-requirements-from-1-january-2023/
In short you are required to do ground training:

Full credits as regards the requirements to undergo a training course prior to undertaking the theoretical knowledge examinations and the skill test to holders of an airline transport pilots licence (‘ATPL’) issued by or on behalf of a third country in accordance with Annex 1 to the Chicago Convention provided that those holders have completed the experience requirements for the issue of an ATPL in the relevant aircraft category as set out in Subpart F of UK Part-FCL and provided that the third country licence contains a valid type rating for the aircraft to be used for the ATPL skill test.

Then you complete some exams and do a skills test

Pass the ATPL skill test on type in accordance with UK Part-FCL (UK CAA Certificated Examiner on UK CAA approved simulator).


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Why are the wings of most passenger jets on the bottom?
I have always wondered why most manufacturers put the wings on the bottom of commercial jets. Help would be appreciated.

Hm, while that should be a duplicate, the answers don't really address jets.

@JanHudec I think the only thing to add for transport jets is "and if you have an uncontained engine failure the bits of the engine will hit the wing instead of the passengers" -- or are there other characteristics you think are worth discussing separately?

Another related question: Why do (almost) all military transports have high wings and civilian transports low wings?

Another related question, with more answers: Why is there really only one basic design for passenger airplanes?

I couldn't find any similar questions. Sorry.

low wings with underwing-mounted engines are easier to service - routine oil refill, filter inspections, leak inspection etc.


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What is the ICAO 24-bit code used for?
I know that each transponder is linked to a unique 24-bit code assigned by ICAO. But to be seen by the Secondary surveillance radar the pilot set the squawk code (4 digit octal code) on the transponder as dictated by the Air Traffic Controller (ATC).
So, why do I need a ICAO 24-bit code? Has it any utility during navigation, or just during maintenance to identify the single transponder (and the aircraft associated)?

In short: the 24 bit address is critical on the technical layer of Air Traffic Control, but it is not used in the operational level. For identification of aircraft and association to flight plans, the air traffic controllers and the flight data processing systems rely mostly on the Mode A code and the aircraft ID (call sign) transmitted by the transponder.

The ICAO 24-bit aircraft address is an essential element of the way Mode S radar and TCAS work.
Before Mode-S radar, only modes A and C were used by civil ATC secondary radars.
Mode A and Mode C are unaddressed; every transponder receiving a Mode A or Mode C interrogation will reply*. This causes two problems, garbling and FRUIT.
Garbling is caused by the overlap of replies from multiple transponders. A transponder replies on 1090 MHz in the from of a number of pulses. For Mode A & C, there are at most 12 pulses between a set of framing pulses. When multiple aircraft reply to the same interrogation, these pulses mix up and it becomes difficult to find out which transponder sent which pulse. This leads to false altitudes or false squawk codes.
FRUIT (False Replies Unsynchronised to Interrogator Transmission) is caused by replies that are triggered by other radars. When multiple radars operate in an area, transponders can be quite busy and the radar is easily mislead by a reply to another radar. In addition to the timing (range) being wrong, the reply can be Mode A (squawk code) while the radar interrogated Mode C (altitude). There is no way to see what kind (A or C) reply was sent.
To overcome these problems of Mode A/C, Mode S was introduced. Mode S is quite different from Mode A/C and requires a more sophisticated radar and transponder. It uses the 24 bit address to distinguish responses from various aircraft and to interrogate specific aircraft.

Most Mode S interrogations are addressed; the interrogation contains the unique 24 bit address of the aircraft it is interrogating. This reduces the probability of garbling since other aircraft will not reply
Unaddressed Mode S interrogations will solicit replies that contain the address of interrogator (radar). This prevents FRUIT since the radar can verify that the reply is correctly addressed.
Unlike Mode A/C which does not have any error checking, a Mode S reply contains a 24 bit CRC check code.
Mode S Altitude and identity (squawk) replies have their own identifier so they can be distinguished.
Mode S radars can be operated in clusters and coordinate between them who is interrogating which aircraft at which time. This further reduces the message load and garbling / fruit probability.

For TCAS, the Mode S address is used to distinguish replies for various aircraft in the vicinity of the own aircraft. The TCAS transponder interrogates omnidirectionally (in all directions) and get's replies from all direction. Again, this is very susceptible to Garbling and FRUIT. Whilst TCAS can work with Mode A/C, for its reliability and coordination of resolution advisories, the 24-bit address is crucial.

Not quite related, but I'll mention that one technique to reduce FRUIT (in all modes) is to compare the return from two successive radar "pings", and throw out returns that do not appear at the same distance from the radar. This is because two different interrogations from the same radar will result in the same signal timing, while replies form other radar's interrogations are very highly likely to appear "randomly" in time.

@ymb1 If a Mode S interrogator does an 'All call' interrogation (i.e. not addressed to a specific aircraft), the address of the interrogator (II/SI code) is included in the interrogation message.. The replying Mode S transponders will then include that code in their  reply. The receiver of such a reply can then check whether the message has the correct II/SI code. If not, it is FRUIT.

The 24-bit address is used primarily in the low-level radio protocol between the surveillance radar and the transponder. The stationary radar encodes this address in its radio ping to specify that it wants a reply from that particular transponder, and all other transponders in the air will then not flood the downlink frequency with replies of their own.
This is what the S in "mode S" stands for: selective interrogation of transponders.
(From time to time a mode S radar will also issue pings that invite every transponder that hears it to reply, in order to learn of new aircraft entering its range of vision. But this can happen much less often than the everyone-respond pings of the old mode A/C protocol).
The 24-bit address is generally not used in higher layers of the system than the physical access layer; these use either mode A squawk codes or alphanumeric callsigns (aircraft ID) that are given in the Mode S response.

24-bit addresses are also used for ADS-B broadcasts -- partially because they reuse the Mode S data format where it is already present; partially because it is a more permanent identifier than callsigns or squawk codes, and therefore is useful for ground equipment to figure out which broadcasts come from the same aircraft.

The ICAO 24-bit code is used by Mode-S Transponders. Secondary Surveillance Radar (SSR) can query Mode-S transponders to not only send the Squawk Code and Altitude Information, but also the callsign or registration set in Mode-S transonders. This way you are able to use non-discreet codes within an airspace and still know which aircraft is which.
Example: In the German Langen Airspace (West of Germany), VFR traffic is assigned SQ Codes 3704 or 3703 when they call in for Flight Information Service. This way, the FIS specialist immediately knows which aircraft are on his frequency and can call them up, but he can still call them by the registration or callsign, as the Mode-S transponder not only transmits the squawk code (Mode-A), but also the registration and callsign (Mode-S). Some countries also use the Mode-S Downlink capabilities to correlate flightplans to aircraft targets and assign the code 1000. This frees up discreet squawk codes.
Related questions:
Is there a relation between the Mode 3/A Code and the ICAO aircraft address?

The 24 bit address is assigned to the aircraft, not to the transponder. If you change the transponder, you have to set the correct 24 bit address assigned to the aircraft in the transponder.

@DeltaLima Corrected, thanks.

For confirmation (although indirect) see for example the bottom of page 4 of this FAA document


text:
Which are the alternatives to EICAS or ECAM?
I know that ECAM and EICAS are the systems for Airbus and Boeing for the monitoring of the aircraft systems. So, on a A320 there is the ECAM and on a B737 there is the EICAS. I know the differences between them and how they work.
What I wonder is:
How do I know in a not Airbus/Boeing aircraft which is the system for the monitoring of aircraft alarms?
For example: what do I have in a AW139, or in a Gulfstream650? Is it still called ECAM or in some other ways? Is it built by the same manufacturer? Has it the same name?

For the Gulfstream at least, it is a proprietary product developed with Honeywell called PlaneView. In general, these systems are called "Electronic Flight Information Systems" or EFIS for short. For larger aircraft they are usually manufacturer specific. For smaller GA aircraft they are provided by the avionics manufacturer, like the Garmin G1000.


text:
Why is kerosene used in Aviation industry for turbogas and turboprop?
Which are advantages (and disadvantages) compared to gasoline or petroil?

Putting 100LL or 100UL in a turboprop is a good way to blow it up. Putting Jet-A in a piston engine is a good way to keep it from running, typically during take-off. Different fuels have different properties that are matched to the type of combustion that they perform.

@RonBeyer -- 100LL in a turbine can be tolerated under some conditions (most smaller gas turbines can digest it AFAIK).  However, Jet-A really makes spark-ignition engines unhappy campers!


text:
Is it legal to accept money for flight training as a gift?
If John offers to pay for Jane's PPL flight training, and Jane accepts it, is she violating rules against compensation? If so, is it feasible to get some kind of waiver? Does it matter whether or not John also acts as her instructor?

Your last edit makes a huge difference to the answer.

@DJClayworth the "payment" to "money" change, or adding the question about John being the CFI?

The instructor part. I'm having to think about the answer.

I don’t see any issue here at all.  John either has his own AC or rents from an FBO, which he is entitled to do so long as his rental agreement with the FBO does not preclude offering instruction.  John is free to offer flight instruction for free.  His financial gift to Jane is his direct operating costs of his own plane, or the rental fee of the FBO plane.  Jane is at no point in any of this transaction being compensated for being PIC, because she is not PIC, she’s not even a P.  This issue is really one of tax treatment and in the US, gifts of up to 15k a year are a non-issue.

@MaxR the potential problem is when she solos. It appears that that isn't an issue either, though.

The question for me is whether John (as the instructor) is receiving any benefit from teaching Jane other than the money (which he is providing anyway and therefore isn't a benefit). I don't think so, but I'm not completely certain.

@DJClayworth Don't flight instructors get PIC time from dual instruction?

John has paid the entire cost of each flight (and more probably) so he isn't getting any benefit from the arrangement, at least just in terms of flight time. If he wanted PIC time he could get it cheaper by paying for a solo flight himself.

In my opinion, this is possibly legal, but depends on the totality of the circumstances. From the Hancock interpretation (emphasis mine):

An item of value is not compensation under the regulations, however, unless the pilot's receipt of it is contingent upon the pilot acting as pilot in command of an aircraft. If you loan your aircraft to a private pilot who pays the expenses associated with the operation of the flight (e.g. fuel) and you are placing no obligation on the pilot (e.g. ferrying your aircraft to a specific location), then it is unlikely that the private pilot would be considered to be acting as pilot in command of an aircraft for compensation or hire. We note that whether a private pilot is receiving something of value in exchange for acting as pilot in command is determined on a case-by-case basis and depends greatly on the purpose and objective of the flight.

If John makes a gift to Jane of $10000 to be used for flight training, with no other restrictions, John is not requiring that Jane act as PIC (as she can use it for dual training or solo, at her discretion), and is not gaining anything in return. As long as it is a bona fide gift and not some attempt to end run around the regulations, it is not against regulations, in my opinion.
The last sentence in the quote is important, though. If, for instance, John stipulates that the flight training must take place in his blimp, which he puts advertisements on, this is definitely not legal. Nobody can say whether this situation is legal or not without all the details.
John acting as the flight instructor makes this a great deal shadier. In particular, as CFI John would have a great deal of control over the flights flown, and John is receiving something of value in return (time building, if nothing else). Dual instruction may still be fine, but John should be very wary of paying for Jane's solo flights, since as her CFI he will be placing a great deal of obligations on Jane as the pilot.

It's completely legal because it's a one way transaction - provided the payment is a genuine gift with absolutely no strings attached.
Private pilots are forbidden from receiving "compensation" - i.e. payments in return for services. Jane is not providing any kind of service in return for the payment, so there is no violation of the rules.
Now there might be a suspicion that this is some kind of under-the-table deal where Jane is in fact providing services in return for the gift, but if that's not the case then there is no problem with legality.
My evidence for this is that it happens all the time. Plenty of trainee pilots accept gifts from family members for their tuition, and if it was illegal then people would be telling them.
I had to think quite a bit about the issue with John being the instructor, but I'm fairly convinced it isn't a problem, because John still isn't getting any benefit from the deal. (He's getting flight time, but he's paying for it so there is no benefit to him, because he could get that flight time just as cheap by just renting the plane a flying solo.) Because of this Jane still isn't providing him with any service. The situation would be even clearer if instead of giving Jane money to hire him as a flight instructor John gave Jane his services for free and payed all the expenses of the instructional flights

@757toga A "gift" is not compensation unless there is something given in return. Building flight time may be considered compensation in some circumstances, but unless there's some quid pro quo it's just a gift, not compensation. In your example, the stipulations Mr. Turel puts on the flights as well as the advertising on the balloon provide the something in return that makes this compensation instead of a gift.

DJ, are you a lawyer versed in this particular field of law? An FAA agent? Making the statement that it's "completely legal" is pretty daring; of course, if the OP follows your advice and finds out different, I guess it's not you who will pay... As for your final paragraph, I live in Northern Virginia and I would guess that 95% of the drivers drive 65+ on I95... doesn't make it legal, and if I told an LEO "but it happens all the time" he'd have a chuckle while giving me my ticket.

I am not meaning to imply that this is legal advice. It isn't.

As for your last point, when people drive 80 on the I95, cops constantly tell them it's illegal (and give them a ticket). When family members give money to people so they can learn to fly you never hear flight schools say "it's illegal for people to give you money to learn to fly". Some organizations offer scholarships for flight training costs (I learned on one) and would know if it was illegal.


text:
Was the first US government-issued pilot license issued in 1927 or '28?

The top image says it was issued April 6, 1928, while the bottom one says April 6, 1927. Are these two different documents issued a year apart, or is there a discrepancy?

Your photos say issued in '27, expires in '28.  What's the question here?

@RalphJ I didn't see that it said "expires." Not sure why I didn't notice that.

His Navy call sign would probably have been "Phil"...

@MichaelHall   <<< Groan! >>>

@MichaelHall what is the significance of the call sign "Phil"?

According to Wiki...
https://en.wikipedia.org/wiki/Pilot_licensing_and_certification
Aero-Club de France began issuing certificates in 1910, retroactive to 1909. Bleriot, Wright Bros are some notables.
https://en.wikipedia.org/wiki/List_of_pilots_awarded_an_Aviator%27s_Certificate_by_the_A%C3%A9ro-Club_de_France_in_1909
Royal Aero Club (UK) also 1910.
https://en.wikipedia.org/wiki/Royal_Aero_Club
Aero Club of America began issuing licenses in 1911. Glenn Curtiss and the Wright Bros, among others.
https://en.wikipedia.org/wiki/Aero_Club_of_America
It seems these were mostly ceremonial, rather than required.


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Can a private pilot flying a passenger to a hospital use a MEDEVAC callsign?
Normal air ambulance flights in medical emergency situations use a callsign consisting of the word "MEDEVAC" followed by the registration number excluding the prefix (e.g. N912MF is "MEDEVAC Niner One Two Mike Foxtrot").
What if a private pilot is using his/her plane, which is not normally used as an air ambulance, to fly a passenger to the nearest hospital in a medical emergency? Can (s)he use "MEDEVAC 123AB" if the plane is N123AB?

I have some FAA advisory circulars still open in a tab from when this question was originally asked. Keep meaning to synthesize them into an answer.

From the AIM 4-2-4:

MEDEVAC flights may include:
(a) Civilian air ambulance flights responding to medical emergencies (e.g., first call to an accident scene, carrying patients, organ donors, organs, or other urgently needed lifesaving medical material).
(b) Air carrier and air taxi flights responding to medical emergencies. The nature of these medical emergency flights usually concerns the transportation of urgently needed lifesaving medical materials or vital organs, but can include inflight medical emergencies. It is imperative that the company/pilot determine, by the nature/urgency of the specific medical cargo, if priority ATC assistance is required.

FAA Order 7110.65AA (the main document that tells ATC what to do) also identifies MEDEVAC aircraft as air ambulances:

Treat air ambulance flights as follows:

Provide priority handling to civil air ambulance flights when the pilot, in radio transmissions, verbally
identifies the flight by stating “MEDEVAC” followed by the FAA authorized call sign or the full civil registration
letters/numbers. Good judgment must be used in each situation to facilitate the most expeditious movement of
a MEDEVAC aircraft.

Or, alternatively, as air taxis/carriers:

The letter “L” is not to be used for air carrier/air taxi MEDEVAC aircraft.

As you are not an air ambulance or an air taxi/carrier, MEDEVAC is not intended for you and is potentially confusing. It's pointless anyway- if you have a medical emergency requiring priority handling, just say that! You'll get the priority handling and you won't confuse ATC into thinking you're an ambulance.

Your answer is better than my old one, deleting.

For a patient who is not an immediate danger of life or some other serious medical emergency, and is just being transported to a hospital for some kind of routine treatment, no, I don’t think that using a callsign like MEDEVAC is appropriate to that flight. If you did have a life-threatening emergency aboard the airplane, it would just simply be far easier to contact ATC and declare an emergency to get priority for that.  Now, there are charity organizations, like Angel Flight West, who transport patients to and from hospitals using general aviation aircraft.  This organization apparently has obtained special permission from the FAA to use the callsign ANGEL FLIGHT and any participating pilot may use this callsign only on flights transporting patients.


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What was the first programmable computer used in a flight-related role on an aircraft?
What was the first programmable digital computer, or device containing a programmable digital computer, used on an aircraft or spacecraft for a purpose related to flight? To use modern devices as an analogy, a GPS navigation system counts, but a passenger, or even a pilot, using a cell phone for non-flight-related purposes does not.

If we're counting spacecraft, maybe the guidance computer on Gemini spacecraft? That was certainly an early one, if not the first.

@Chris yeah, I would count that

The first digital avionic computer was not "programmable" in the same way we understand the term today. The F14 Tomcat used a fully digital flight control system but the "computer" did not execute any instructions. Instead they were blocks of digital logic (adders, multipliers, multiplexers, integrators etc.) that were connected together to calculate algorithms. So it was fully "parallel" (or rather fully pipelined) because it calculated all the numbers with each tick of the clock. It was digital though..

.. performing electronics operations/calculations on numbers instead of current and voltages (like traditional analog circuits)

The Gemini guidance computer was the first computer used on a spacecraft. It had 159744 bits of memory, a 7143 Hz clock, and weighed about 60 pounds.
The computer was used to effect the first successful rendezvous of spacecraft, between Gemini VI and VII. It also allowed for more precise control on reentry than was previously possible.
Other navigation in Gemini was primarily done by reference to ground networks, but the guidance computer was capable of navigation if connection to ground networks was lost.